In recent years, increasing interest has been shown in recovering oil contained in oil shale and other similar hydrocarbon-containing solids by heating the solids to an elevated temperature in a retort to free the oil. In many of these processes, the oil is recovered from the retort in the form of a vapor and these vapors usually contain significant amounts of entrained shale fines. Some of the fines can be removed from the vapor by cyclone separators; however, the ultimate shale oil liquid still contains too high a concentration of entrained shale fines for acceptable downstream processing.
Particular examples of retorting processes include those described in U.S. Ser. No. 802,999, filed June 3, 1977, now U.S. Pat. No. 4,157,245 which discloses an indirectly heated retorting process in which fluidized heat carrier material flows countercurrently to entrained shale or coal particlees introduced at the bottom of the retort; U.S. Ser. No. 811,496, filed June 30, 1977, now U.S. Pat. No. 4,133,739 which discloses a directly heated retorting process in which fluidized heat carrier material flows downwardly and countercurrent to entrained hydrocarbon-containing particles introduced at an intermediate portion of the retort; U.S. Ser. No. 891,084, filed Mar. 28, 1978, now U.S. Pat. No. 4,183,800 which discloses an indirectly heated retorting process in which heat carrier material is fluidized and shale or coal particles, introduced at an intermediate portion of the retort, are fluidized in part and entraind in part (all to Mitchell et al); U.S. Ser. No. 889,156, filed Mar. 22, 1978 to Tamm et al, which discloses an indirectly heated retorting process in which fluidizable and non-fluidizable shale or coal particles and heat carrier particles are passed downwardly through a retort; U.S. Pat. No. 4,056,461 to Unverferth, which discloses an indirectly heated process in which hydrocarbon-containing particles are mixed with heat carrier particles and conveyed through an elongated retort by a rotating helical coil; U.S. Pat. No. 4,087,347 to Langlois et al., which discloses an indirectly heated shale retorting process in which shale particles are retorted with heat carrier material in a lift pipe and stripper vessel; U.S. Pat. No. 4,125,453 to Tamm et al, which discloses an indirectly heated shale retorting process in which shale particles are retorted with heat carrier material in a spouted bed; and the Lurgi Ruhrgas "Sand Cracker" process in which shale is retorted in a sealed screw-type conveyor, described in the Synthetic Fuels Data Handbook compiled by T. A. Hendrickson, Cameron Engineers, Inc., 1315 South Clarkson Street, Denver, Colo. 80210, pages 80-82. All of these disclosures are incorporated herein by reference.
One method which has been used for removing entrained particles from gases involves passing the gases through a granular filter bed, such as the one described in the article "Filtration Theory For Granular Beds" by Schmidt et al. in Journal of the Air Pollution Control Association, Volume 28, No. 2, pages 143-146 (February 1978). Commercial application of a granular bed is described in U.S. Pat. No. 4,017,278 to Reese, the substance of which is incorporated herein by reference. Reese describes passing a gas containing finely divided solids through an annular bed of solid contact material which traps the finely divided solids. The contact material containing the trapped, finely divided solids is withdrawn from the bottom of the bed and treated to remove the trapped, finely divided solids before being returned to the top of the granular bed. A large portion of the cost of operating a granular bed with recycled contact material is due to the necessity of treating the recycled contact material for removal of the finely divided solids.